Patent Application
20100216586
1. Field of the Invention
This invention relates to the drive trains for automotive trucks and, more particularly, to apparatuses for readily altering the drive ratio between the drive wheels and engine of mid-size to large trucks.
2. Description of Related Art
All trucks have a variable transmission that can be adjusted throughout a range of selectable transmission ratios to vary the speed of the drive wheels relative to the speed of the engine in accordance with the conditions under which the truck is operating. The lowest ratio at which the drive wheels can be operated is often referred to as the “drive ratio” of the truck. Persons skilled in the art will appreciate that this drive ratio is a combination of all the gear reductions found in the drive train including the lowest transmission ratio as well as the further gear reductions occurring between pinions and large ring/bull gears driving each differential, etc. While most of these gear reductions occur through gear trains positioned within the vehicle's transmission housing and within the differential complexes, in some specialized vehicles there may be a further reduction between the individual drive axles and their respective wheels.
Most trucks, including mid-size and large trucks, have only a single pair of drive wheels mounted on one set of axles divided by a drive-wheel differential. However, many larger trucks have two sets of drive axles positioned in tandem, and each set of drive axles is divided by a respective drive-wheel differential. Further, since the tandem axles of these large trucks do not rotate at the same speeds when the truck is turning or passing over uneven terrain, a torque-divider (e.g., a cam-and-pawl mechanism) having co-axial output shafts is provided to divide the drive torque from the transmission between the two sets of drive axles. Each of these separate drive axles receives driving torque from its respective torque-divider output through a respective gear train that includes a bevel pinion and ring gear combination followed by a helical gear in mesh with a much larger ring gear. This much larger ring gear is often called a “bull” gear and, to clarify identification is referred to herein as a “ring/bull” gear. The respective gear trains are each mounted in a respective cast iron housing sometimes referred to as a “pig”. Thus, each of the two drive axles has a respective “pig” interconnected by the torque-divider.
Since trucks are operated under widely divergent conditions that can vary from carrying relatively light loads over paved roads at fast highway speeds to extremely heavy loads over rutted and soggy off-road terrain, truck manufacturers often provide different models of trucks for various major categories of expected operations, e.g., light or heavy loads, for highway transport, or construction, or refuse hauling, etc. Also, some multi-use models of trucks can be used for widely disparate operations and are sold with any one of numerous selectable drive trains, e.g., drive ratios varying from 3:8 to 9:1 according to the desired operation. Each of these different drive ratios uses a different combination of gearing in the gear-train of the drive axle pig (or in each pig of a tandem-drive truck). The customer selects a drive ratio appropriate for its needs and, if this ratio is not available on a truck in stock, a different truck is ordered by the dealer.
Therefore, dealers usually try to keep a selection of multi-use models available, each truck having a different drive ratio because, if they do not have a vehicle with the desired drive ratio in stock, they have to make a special order from the manufacturer for a model with the desired drive ratio. Owners of fleets of trucks similarly try to keep a variety of drive ratios in their fleets, particularly since only certain drive ratios are reasonably appropriate for some operations. One prior art solution to this problem is disclosed in U.S. Pat. No. 4,437,530 by providing a changeable set of planetary reduction gears affixed to the output end of the final drive between the transmission and the drive wheels.
In a related problem, well known to those skilled in the art, torque-dividers are used in tandem drive-axle trucks because the use of conventional standard differentials is prevented since standard differentials cannot provide the required co-axial output due to the cross-pin that supports the differential's drive pinions. Unfortunately, these prior art torque-dividers suffer from damaging wear, particularly when there are repeated differences between the speeds of the two sets of heavily loaded tandem axles, causing the torque-dividers to slip and resulting in drive-train “chatter”. While this chatter is particularly noticeable at low speeds, it also occurs at all speeds when terrain differences are encountered, causing the vehicle load to alternate between the two sets of axles and resulting in repetitive shocks and undesirable wear throughout the entire drive train of the vehicle.
As will be explained in greater detail below, a preferred embodiment of the invention for use in tandem drive-axle trucks replaces the conventional torque-divider with a limited-slip crossed-axis compound planetary gear differential to divide the input torque between the tandem axles of large trucks. [Those skilled in the art are reminded that, as different from open differentials and limited-slip designs based upon standard differential gear arrangements, differentials using a crossed-axis compound planetary gear complex can provide co-axial outputs, since they do not include a cross-pin to connect the driver pinions.]
While there are many types of traction-assisting differentials, one of the most commercially successful has been the all-gear differentials based upon the designs of Vernon E. Gleasman. This high-bias differential is based upon his crossed-axis design that has been identified commercially as the Torsen®-Type 1 differential. Recent improvements of this high-bias differential using crossed-axis planetary gearing are disclosed in U.S. Pat. No. 6,783,476 (“Compact Full-Traction Differential”) and U.S. Pat. No. 7,542,821 (“Full Traction Differential with Hybrid Gearing”), both assigned to the same assignee as the present invention and identified by the trademark IsoTorque®, and both of those references are incorporated herein by reference.
[NOTE: To avoid confusion, the following explanation of the invention will identify the differential positioned between the drive wheels of each set of axles as a “drive-axle” differential, while the differential being substituted for the torque-divider between the two tandem axle sets of a large truck will be indentified as a “drive-shaft” differential.]
To supplement the detailed disclosure below, reference is now made to
Each pair of combination gears 16 is mounted within slots or bores including mounting shafts 19 formed in the main body of the housing 10 so that each combination gear rotates on an axis that is substantially perpendicular to the axis of rotation of the side-gear worms 14, 15. The spur gear portions 17 of the combination gears 16 of each pair are in mesh with each other, while the worm-wheel portions 18 are, respectively, in mesh with one of the side-gear worms 14, 15 for transferring and dividing torque between the axle ends 11, 12. In order to carry most automotive loads, prior art differentials of this type usually include three sets of paired combination gears positioned at approximately 120° intervals about the periphery of each side-gear worm 14, 15.
For purposes of the invention disclosed herein, the type of crossed-axis differential just generally described above incorporates many of the improvements described in the above-identified incorporated references.
An additional drive train problem with today's fleets of trucks is that, because a large portion of current truck axles are over 30 years old, they do not have the proper axle ratio in order to optimize fuel economy when driving on highways.
The invention disclosed below provides a simple and inexpensive solution for the drive train problems referred to above.
The drive train of a truck is modified by the addition of a single changeable pair of mating gears at the intersection between the output shaft of the transmission and the differential complex, i.e., at the input of the final drive assembly. More particularly, this changeable gear pair is positioned between the output shaft of the transmission and the intermediate gear train that drives the ring/bull gear fixed to the drive-axle differential for a first set of drive wheels. One gear of this changeable pair is releasably connected to the distal end of the output shaft of the transmission, while the mating gear of the pair is releasably connected to the input of either (a) the intermediate gear train of the ring/bull gear (for single drive-axle trucks) or (b) the drive-shaft differential (for tandem drive-axle trucks). Persons skilled in the art will understand that the input to a differential is generally a flange fixed to one end of the housing for providing rotational power.
This single changeable gear pair has helical or spur teeth and, preferably, the gear connected to the distal end of the transmission output shaft is a ring gear with internal teeth, thereby (a) maintaining the same direction of shaft rotation between the gear pair, and (b) permitting minor shaft alignment adjustments between the transmission and rear axle without requiring the use of universal joints. This changeable gear pair is readily and quickly replaceable. Several sets of these changeable gears are preferably maintained in stock (by the dealer or fleet owner) in predetermined ratios so that the drive ratio of the truck is easily and inexpensively alterable by the selection of an appropriate gear pair to accommodate different expected operating conditions.
In addition to the short time required to make the drive ratio change according to the invention herein, the cost of the parts for making this relatively easy change is limited to only a single pair of mating helical or spur gears to interconnect the vehicle drive axle with either the gear-train of the drive-axle pig (of a single drive-axle truck) or the housing flange of the drive-shaft differential that delivers the divided driving torque to each drive-axle pig of a tandem pair. That is, the gear trains of the relatively large pigs associated with drive axles of the trucks do not have to be moved or altered in any way. Dealers or fleet owners need only maintain a varied supply of quick-change gear pairs to readily provide the customer's desired drive ratio.
Another advantage of a changeable pair of mating gears of the present invention is improved fuel economy for the highway driving of current fleets of trucks. As mentioned above, a large portion of current truck axles are more than 30 years old, and a redesign and building of the whole truck axle, costing millions of dollars, would be required to get the proper axle ratio in order to optimize the fuel economy of current trucks driving at high speeds on today's highways. A changeable pair of mating gears of the present invention is capable of providing the higher axle ratio required to optimize fuel economy of current trucks conveniently and inexpensively without redesigning and replacing the whole truck axle.
Also, one preferred embodiment of the invention herein replaces the prior art torque-divider used to divide driving torque between the respective axles of tandem drive-axle trucks with a full-traction differential having a crossed-axis compound planetary gear complex to avoid chatter problems. Recent improvements in the latter differential have shown minimal wear when tested under significant heavy load conditions.
The drive trains of mid-size and large trucks are illustrated schematically in
A larger truck 110′ (such as the trucks used to pull semitrailers) often includes a second set of drive wheels 122′ positioned in tandem with the first set of drive wheels 122. These drive wheels 122′ are similarly mounted on axles 121′ to which driving torque is delivered through a second differential complex 120′ from a divided-drive shaft 126′. Since the distance between the two sets of tandem drive axles 121, 121′ causes the axles to rotate at different speeds when the truck is turning or passing over uneven terrain, the addition of the second set of axles requires the use of a torque-divider 128′ (indicated in dotted lines) to account for these speed differences.
The just-described portion of the differential complex 120 that interconnects the bull gear 140 with the drive shaft 118 is referred to collectively herein as an “intermediate gear train” having differentially-divided input provided by a drive shaft.
The second divided-drive shaft 126′ delivers the differentiated drive to a differential complex 120′ that, while not shown separately in detail, is substantially identical to the just-described differential complex 120 except that it omits a torque-divider 128′. That is, as illustrated in
As indicated above, the drive-shaft differential 228 is a recently improved full-traction crossed-axis compound planetary gear differential preferably having the IsoTorque design characteristics described in the above Description of Related Art (and more fully disclosed in the above-identified documents incorporated by reference). In actual practice, this type of prior art differential does a remarkable job of preventing undesirable wheel slip under most conditions. In fact, one or more of these traction-assisting differentials are either standard or optional on vehicles presently being sold by at least eight major automobile companies throughout the world, and there are two of these differentials in every U.S. Army HMMWV (“Hummer”) vehicle (one differentiating between the front wheels and the other between the rear wheels).
All prior art crossed-axis differentials are presently referred to as “limited-slip”, and almost all of those that are presently being manufactured and sold are designed with relatively low torque bias ratios, no greater than 5-to-1. However, while the recently improved differentials described in the incorporated references can be designed with torque bias in that same range, they are preferably designed for torque bias ratios greater than 5-to-1. Therefore, these recently improved differentials are often described as being “full-traction” to distinguish their higher bias from other prior art crossed-axis differentials. Further, these improved differentials are significantly more compact, being smaller in both size and weight, and they avoid thrust duplication between the side-gear worms. They are also less costly to manufacture than earlier designs of other prior art crossed-axis differentials, while still fully meeting similar load-carrying specifications.
With regard to the drive-shaft differential 228 illustrated in
It is assumed that a particular changeable drive-ratio gear pair 352, 354 has been selected having a predetermined gear-ratio that is appropriate to alter the drive ratio of the illustrated drive train to accommodate an expected operating condition. (As indicated above, the invention contemplates that the truck dealer or truck fleet owner maintains a stock of changeable mating pairs having various predetermined gear-ratios and has selected an appropriate predetermined gear-ratio for the gear pair 352, 354.)
The selected changeable mating helical gears 352, 354 are joined to the drive train of the differential complex 320 by releasable connections that are only indicated schematically in
In regard to this second embodiment including the invention's quick-change apparatus shown in
When equipped with the inventive drive just described above, the versatility of prior art truck 110′ (
The invention has just been described in a drive train for use in a larger prior art tandem drive axle truck 110′ (
The selected changeable mating helical gears 452, 454 are joined to the drive train of the differential complex 420 by releasable connections that are only indicated schematically in
In regard to this third embodiment including the invention's quick-change apparatus shown in
Preferred embodiments of the invention's quick-change assembly are illustrated in
As just indicated above, the use of an internal ring gear as part of the changeable gear pair provides the additional advantage of a greater adjustability of the drive train alignment when used to alter the drive ratios of existing vehicles. Referring to
In existing trucks, the center of the transmission drive shaft and the center of the input for the existing differential complex of the drive axle for the truck are both fixed in space. The distance between these two centers often varies from truck to truck. Therefore, for any given changeable gear pair 552, 554, these center distances can vary any where within circle of adjustability 560 and rotary connection between the transmission and drive axle can be accomplished without the necessity of a normally required universal joint apparatus.
Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.
This application claims one or more inventions which were disclosed in Provisional Application No. 61/155,366, filed Feb. 25, 2009, entitled “QUICK-CHANGE TRUCK AXLE”. The benefit under 35 USC §119(e) of the U.S. provisional application is hereby claimed, and the aforementioned application is hereby incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61155366 | Feb 2009 | US |
